This invention relates generally to fluid flow control systems and is concerned more particularly with a calorimetric measuring system having means for maintaining a uniform flow of fluid through a calorimetric load.
A fluid flow system generally includes a pressurized fluid source operatively connected through a control means to a load. The load usually is suitably connected to an exhaust means which may discharge spent fluid from the system or return it to the source for recirculation through the system. Generally, the control means includes a flow regulating valve and means for indicating the rate of fluid flow through the load.
A system of the described type may comprise, for example, a calorimetric measuring system having a fluid reservoir suitably connected to a constant displacement pump. The pump provides pressure generating means for maintaining a uniform rate of fluid flow through a control means and a connected calorimetric load. A typical load may comprise an electrical power consuming device thermally coupled to a chamber through which the fluid flows to an exhaust means. Thus, the temperature of the fluid adjacent the entrance and exit portions, for example, of the chamber may be measured to obtain a temperature differential which is a result of energy transmitted to the fluid from the electrically powered device under test. The temperature differential and the rate of fluid flow through the chamber yield a determination of the electrical power being consumed by the device under test.
The temperature differential initially obtained may be too low in value to yield a sufficiently accurate determination of the electrical power being consumed. However, by slowing the flow of fluid through the load, a greater quantity of energy will be transmitted from the device under test to each unit volume of fluid passing through the chamber. Thus, a higher temperature differential value may be obtained by adjusting the control means to decrease the rate of fluid flow through the calorimetric load. This decrease in flow rate, on the other hand, is not compatible with efficient operation of the constant displacement pump, which is designed to force a predetermined quantity of fluid per unit time through the control means. Therefore, attempts have been made to achieve compatibility by providing a control means suitable for adjusting the rate of fluid flow through the load and permitting efficient operation of the constant displacement pump.
Generally, prior art systems of the described type include a control means comprising a manifold arrangement having, in addition to the load outlet and associated control valve, at least one bypass outlet and associated bypass valve. The bypass outlet usually is suitably connected to a bypass line which may discharge excess fluid from the system or return it to the fluid reservoir for recycling. Thus, when the control valve is adjusted to decrease fluid flow through the load, the bypass valve may be adjusted to increase fluid flow correspondingly through the bypass line. The inverse adjustments of the control valve and the bypass valve should be accomplished simultaneously in order to avoid generation of excess pressure by the pump, which may rupture or otherwise damage the connecting fluid line. However, simultaneous adjustment of the two valves is difficult to accomplish without resorting to the use of sophisticated automatic equipment which increases the cost of the system prohibitively.
Therefore, it is advantageous and desirable to provide a fluid flow system of the described type with inexpensive control means for simultaneously varying the rate of fluid flow through the load and through a bypass line in a smooth transitional manner.